Direct-coupled designs—those that connect one circuit stage to the next without a capacitor—are often praised for their clarity, immediacy, and openness. And for good reason. Anytime we put a component between the music and our ears, it leaves a fingerprint.
A capacitor’s job is to block DC while allowing AC to pass. Since audio is alternating current, it can travel through the capacitor. But the process isn’t quite transparent. A capacitor doesn’t conduct AC like a wire—it stores and releases energy. It charges and discharges in response to the signal. That means the signal gets “translated” into an electric field, then back again.
This introduces problems.
For starters, capacitors are frequency-dependent. Their impedance (opposition to current flow) decreases as frequency increases. At low frequencies—think deep bass—a capacitor may begin to resist the signal more, causing phase shift and amplitude roll-off. This can result in subtle timing smear or even a thinning out of the bottom end.
There’s also dielectric absorption, where the insulating material inside the capacitor temporarily holds on to some energy, then releases it slightly delayed. That stored and re-emitted energy wasn’t in the original signal—and it adds a kind of haze. It’s like echo or ghosting, only in micro-detail.
Now, in many circuits, coupling capacitors are necessary. They keep DC offset from building up and damaging downstream components. But when you can design around them—using direct coupling and servo mechanisms to handle offset—you’re removing a potential bottleneck.
Fewer translation layers between source and output.
And in audio, that usually means getting closer to the truth.
